texts: Why the blank wedges in this very early 21 cm map of the Milky Way? (Oort et al. 1958)

texts:
Jan Oort was a pioneer in radio astronomy. Wikipedia says:

  It has been written that “Oort was probably the first astronomer to realize the importance” of radio astronomy. “In the days before radio telescopes,” one source notes, “Oort was one of the few scientists to realise the potential significance of using radio waves to search the heavens. His theoretical research suggested that vast clouds of hydrogen lingered in the spiral arms of the Galaxy. These molecular clouds, he predicted, were the birthplaces of stars.”

The article includes the image shown below, which is a 21 cm radio map of the Milky Way galaxy. (for more on the transparency of dust at 21 cm see this excellent answer to How was the galactic plane established?

You can also read more about Oort's work during this time in this 1976 AIP Oral History Interview interview.

I'm guessing that the center of the plot is the galactic center and the point at 8 kpc above it is the Earth. What is the reason for the two blank wedges, projecting downward and upward from the Earth? Are they geometrical, blind spots from the few early radio telescopes in the 1950's perhaps, or do they reflect real phenomenon in the galaxy?

The original source is The galactic system as a spiral nebula Oort, J. H.; Kerr, F. J.; Westerhout, G. MNRAS 118, (1958) p. 379


texts: Excluding a rectangular region from an image in FITS

texts:
I am a complete beginner in astronomy. While learning DS9, I came up with the following question.

Say I want to exclude a boxed region from an image FITS. The corresponding parameters according to Chandra is

Box = (xcenter,ycenter,width,height)
Box = (xcenter,ycenter,width,height,angle)

Although the name is self-explanatory yet I am confused about their respective units. What unit is used to label these parameters?


texts: How important is where you get your PhD?

texts: I know that in some fields it is very important to earn a PhD from a top school if your goal is to achieve competitive postdoc offers. How true is this in pursuing a career in astronomy/astrophysics? How possible is it to have a successful career (e.g to achieve a highly-paid, tenured faculty position in a great department) with a PhD from a mid-rank school? I would love any insights from early-career astronomers.


texts:
How is rain related to earth rotation? Suppose the earth rotation slowed down gradually to a third of its current speed. Will that affect the rain? If the earth stopped rotating on its axis completely, will the rain stop altogether?

Thank you.


texts: How many judges sat on Galileo's trial and who were they exactly?

texts: I saw several chronologies of the trial online but most of them only mention the name of Urban 8 as involved in the actual court proceedings. How many judges were involved and who were they exactly? Some useful information can be found here.


texts: Existence of planets larger than their host star?

texts:
The mass region of objects between ~ 0.5 Jupiter masses and 80 Jupiter masses (gas giants through to brown dwarfs and red dwarfs) is typified by an almost flat relationship with object diameter. There are planets out there which are larger than some of the smallest stars.

The smallest (currently fusing) star known, EBLM-J0555-57, is estimated to be slightly larger than Saturn (at about 59000 km radius with 85 times Jupiter's mass).

One of the largest planets known that isn't a suspected brown dwarf, WASP-79b is estimated to be twice Jupiter's diameter at 0.9 times Jupiter's mass. Many Hot jupiters and puffy planets with similar measurements are known.

How likely are there to be systems where a planet is larger than its host star? Are there any examples known?

I am looking for currently fusing stars only, which rules out pulsar planets, etc.


texts: Could the dinosaurs have seen the asteroid that killed them?

texts:
Wikipedia says the Chicxulub impactor is thought to have been a 10-15 km diameter object. Would it have been visible to a (human*) naked eye before impact? And if so, would it have appeared like a star that grew brighter and brighter each night?

* I know, there were no humans at the time.


texts: Is normal matter always accompanied by dark matter and vice versa?

texts:
Is normal matter always accompanied by dark matter and dark matter by normal matter?

Was ever observed effect of gravity lensing without normal matter?


texts: Can someone explain a Geostationary Orbit in a simpler way?

texts:
According to Wikipedia (link),  a geostationary orbit, geostationary Earth orbit or geosynchronous equatorial orbit (GEO), is a circular orbit 35,786 kilometres (22,236 mi) above the Earth's equator and following the direction of the Earth's rotation. An object in such an orbit has an orbital period equal to the Earth's rotational period (one sidereal day), and thus appears motionless, at a fixed position in the sky, to ground observers.

My question is then couldn't any orbit be a GEO? I mean, what about a satellite in an orbit that's say 70,000km, if the angular speed of the satellite was the same as the earth's rotation such that it always stayed in a fixed position when observed from the Earth, then isn't that a GEO orbit as well?


texts: Are any bow shocks seen in the visible spectrum?

texts:
Are any of the images of bow shocks created from visible light, or are they all from infrared light?  While I'm including two of the better known images, my question is about any known bow shock.

LL Orionis

Zeta Ophiuchi

Source of image-Wilipedia


texts: How do we define "up and down" in space?

texts: Every model of the solar system seems to follow a specific orientation in which the upper side of the system is Earth's north half and the lower side of the system is Earth's southern half. So is North and South in space, or up and down based on Earth's up and down?


texts: What would the effects on or around Earth if Betelgeuse went supernova?

texts:
There's been a lot of news lately about Betelgeuse possibly exploding sooner than perhaps was expected. Some examples:

Guinan, Edward F.; Wasatonic, Richard J.; Calderwood, Thomas J. (8 December 2019). "ATel #13341 - The Fainting of the Nearby Red Supergiant Betelgeuse". The Astronomer's Telegram. Retrieved 27 December 2019. (Link)
Guinan, Edward F.; Wasatonic, Richard J.; Calderwood, Thomas J. (23 December 2019). "ATel #13365 - Updates on the "Fainting" of Betelgeuse". The Astronomer's Telegram. Retrieved 27 December 2019. (Link)

What would the effects on Earth be if Betelgeuse were to explode within our lifetimes?

Of course, this would be highly unlikely to happen during our lifetimes, but I'm curious what sorts of effects, if any, it might have on our planet (including our upper atmosphere). I imagine the effects would be measurable but negligible.

I'm looking for imaginative but scientifically-based answers.


texts: What are the steps I have to follow to join SETI programe from my location (India)?

texts: I just want to know if I can be part of SETI project. I have gone through SETI website but still didn't get enough guidance. Apart from installing boinc software for letting my machine used as part of seti , is there any other way round through which I can explore something about Extra terrestrial life whether through institutions or as part of any community, I simply do not want to be part of community which believe green men are visiting earth but want to part of genuine one. I can give inputs in computing , programming , communications as engineer.


texts: I see a non flickering star. How is this possible?

texts: I looked outside my window one night, and the moon was shining brightly, and it wasn't a full moon. But thats not the point. Really close to it was something that looked liked a star. It was really bright, and it gave off a white light, but the more I looked at it, the more I realized that it wasn't flickering or twinkling the way stars do. A few minutes later, I looked at it again, and this time it was smaller, less bright, and farther away from the moon. I know its not a satalite because I've seen those before and they move faster, and they give off the same amount of light all the time. If anyone has any idea what this thing could be, please tell me, because I really want to know.


texts: Is cosmological redshift caused due to expansion of space or distance traveled by light?

texts:
If the universe wasn't expanding, would light still be redshifted after traveling some distance?
Is there a way of being sure that it's the expansion that causes light to redshift and not just a natural phenomenon for light to redshift as it travels, regardless of whether space is expanding. In the latter case, the only way expansion of space could affect the redshift would be by making light travel a longer distance.
Edit: So I've come across the term 'Tired light' in an SE answer but it doesn't really explain why there aren't supporters for this theory. So, why aren't there?


texts: Many people concern themselves with understanding the Galactic potential. To me, the most obvious way is to measure the acceleration of a star, as this is directly related to the potential. So, one could measure a LOS velocity (or proper motion) at different years and measure its change. I understand that orbital timescales of stars are huge however, so can this be done? If not, how far (order of magnitude) away are we from having the required uncertainties for achieving this?


texts:
I think I just saw a supernova explode with my own eyes through my GSO 12 inch Dobsonian. Please tell me what it was! I am still trying to find what it was it was mindblowing!
I went out on my roof around 18:20 (New Delhi, India) and was looking up thinking we are going to have clear skies tonight.
Suddenly I could see the bright star without the telescope and I was surprised to see such a bright object near zenith so I ran in and got my telescope out.
When I looked through the scope It was looking like a bright bubble very shiny and the outer surface seemed brighter. I thought my collimation was out so I collimated the scope and it was not too off.
After collimation, I could see a small object in orbit around the star/object. As I continued to observe it, it suddenly exploded like fireworks and tiny particles shining very brightly started to swirl in waves and dimmed quickly. This was around 18:38 I took pictures with my phone through the eyepiece and the sky was still lit and blue in colour.
The below pics are edited in snap seed on my phone.


texts: How many things are wrong in this "artist view" of the TRAPPIST-1 system?

texts:
There is a this poster on the NASA site

(

that irks me. Of course its an artist's fantasy, but since it is on a NASA site, I see people considering it as scientifically accurate. So, beyond the two obvious "In which direction(s) is the sun", and "OMG these two planets are crashing into each other! Before we crash in the debris!", what else is wrong? Tides? Roche's limit? Atmospheres ripped out?

Also, since 1e is an intermediate planet, it is possible to have the other six planets all conveniently placed in the same area of the sky?


texts: Could the Sun have liquid iron in orbit?

texts: How close of an orbit to the Sun could an iron meteor get before it melts into a ball?


texts: How many Supernovae have been Imaged in the Hubble Ultra-Deep Field?

texts:
The Hubble Ultra-Deep Field is an image showing about 10.000 galaxies:

2
Image Credit: NASA

Consider Victor Buso's spectacular discovery of an early supernova in NGC 613 (named SN 2016gkg):

4
Image Credit: Carnegie Institution for Science/Las Campanas Observatory/UC Santa Cruz

This got me wondering about how many supernovae the Hubble Ultra-Deep Field may contain without us knowing because we would need a light curve or reference image to identify one with certainty. Some supernovae also would be only a pixel or less and impossible to identify.

Is it possible to calculate a meaningful lower bound?


texts: What is the actual black hole merger speed?

texts:
I have seen models of 2 black hole mergers.

https://www.theverge.com/2017/11/16/16665132/gravitational-waves-ligo-virgo-black-holes-merger-multi-messenger-astronomy

When we see a space ship appear to be frozen in time as it approaches the event horizon then would a back hole merger be faster then perceived in our time?

John put it well in the comments:  People say merging black holes end up moving at half the speed of light, but don't say anything about the gravitational time dilation wherein the "coordinate" speed of light goes to zero at the event horizon. Which would mean black holes would have to be moving faster than the local speed of light. How can this be right?

Can things move faster than light inside the event horizon of a black hole?


texts: Are there neutron stars whose magnetic axis and rotating axis are the same, and if so what will happen?

texts:
I know that there's probably a higher chance of having a neutron star that has its magnetic axis inclined to the rotational axis rather than having it perfectly aligned.
If they are not aligned, the neutron star will create beams of radiation that sweep through space like the beams of light from a lighthouse. But what will happen if they were to be aligned?


texts:
Writing this answer got me thinking.

As far as I understand it, stars themselves radiate most of their energy at optical wavelengths (near-IR through near-UV).

Various types of stellar objects may flare in various ways when in-falling matter from an accretion disk or companion is heated in magnetic fields or undergoes transient nucleosynthesis, but I'm excluding these types of processes and asking only about radiation from the stellar object itself, in steady-state.

Question: How far have individual stars been seen by radio telescopes?


texts: Closest path of solar eclipse central line

texts:
I'm trying to calculate the closest path of the center line of a given eclipse at a given time by using its besselian elements; However i'm getting an error range up to 30 km (18.6 mile) in the worst case and 5 km (3.1 mile) in the best case (both cases was compared with F. Espenak prediction)
Lets use eclipse of August 12, 2026 at 18:00 UTC.
F. Espenak prediction: 58°16.1'N   021°34.4'W (58.2683, 21.5733)
My prediction: 58°16.8'N 21°47.4'W (58.2795, 21.7901)
The difference is close to 13 km (8 mile) which is too big for my application so I need to refine/review the procedure/algorithm I'm using.
Calculus
Given the following besselian elements:
e20260812 = {
    t0: 18.00, At: 72.3,
    x0: 0.475510, x1: 0.518923, x2: -7.727e-05, x3: -8.039e-06,
    y0: 0.771185, y1: -0.230167, y2: -1.246e-04, y3: 3.767e-06,
    d0: 14.796683, d1: -0.012065, d2: -3.098e-06, d3: 0.0,
    l10: 0.537974, l11: 0.000094, l12: -1.212e-05, l13: 0.0,
    l20: -0.008142, l21: 0.000093, l22: -1.206e-05, l23: 0.0,
    u0: 88.747810, u1: 15.003090, u2: 1.764e-06, u3: 0.0,
    tanf1: 0.004614,  tanf2: 0.004591
}

(At represents $\Delta T$)
0 - Reference timestamp.
Where t1 = 18.00
t = t1 - t0 + At/3600.0

1 - Time dependent calculus
x = x0 + x1 * t + x2 * t^2 + x3 * t^3
y = y0 + y1 * t + y2 * t^2 + y3 * t^3
d = d0 + d1 * t + d2 * t^2 + d3 * t^3
u = u0 + u1 * t + u2 * t^2 + u3 * t^3

2 - Location dependent calculus
Initially I'm using ro=1.0 and following the below sequence to obtain an approximation of phi, which is the Latitude.
ro = 1.0
e = 0.0818192 // earth eccentricity
sin_d = sin(d * pi / 180.0)
cos_d = cos(d * pi / 180.0)
zeta = sqrt(ro^2 + x^2 + y^2)
cos_theta = (-y * sin_d + zeta * cos_d) / ro
sin_phi_1 = (y * cos_d + zeta * sen_d) / ro
cos_phi_1 = sqrt( (x/ro)^2 + cos_theta^2 )
phi_1 = asin(sin_phi_1) / pi * 180.0
phi = atan(sin_phi_1 / cos_phi_1 / sqrt(1 - e^2)) / pi * 180.0

At this point phi = 58.1224 for 18:00 hs UTC.
Once phi was calculated, we recalculate ro as follow to get a better approximation of phi and varpi (not yet calculated)
sin_phi = sin(phi * pi / 180.0)
ro1 = sqrt( (1 - 2e^2 * sin_phi^2 + e^4 * sin_phi^2) / (1 - e^2 * sin_phi^2) )

Applying the updated ro (now ro1), we update sin_d and cos_d as follow:
sin_d1 = sin_d / ro1;
cos_d1 = sqrt(1-e^2) * (cos_d / ro1)

And update zeta and cos_theta
zeta1 = sqrt(ro1^2 + x^2 + y^2)
cos_theta1 = (-y * sin_d1 + zeta1 * cos_d1) / ro1

Finally we calculate vapri (the Longitud) as follows:
tan_theta = x / cos_theta1
theta = atan( tan_theta ) / Math.PI * 180.0
vapri = u - theta * ro1

and recalculate phi by doing:
cos_phi2 =  cos_theta1 / cos(theta / 180.0 * pi)
phi1 = acos(cos_phi2) / pi * 180.0
phi = atan(tan(phi1 / 180.0 * pi) / sqrt(1 - e^2)) / pi * 180.0

At this point phi = 58.2795 , vapri = 21.7901 for 18:00 hs UTC (both values MUST be properly signed but I omitted that trivial part) a significant difference compared with the NASA prediction: 58.2683, 21.5733 (13 km or 8 mile)
My feeling is that ro1 in not good enough precise, so the final results get shifted, but I have no idea at all about how to getting unblocked.
I'm using 64 bit floating point calculator; It is ok for this kind of calculus?
Is this method good enough to get an error range near to 500m? if not, could you provide a method/fix to achieve that aim.
Any help would be appreciated.


texts: Mars night sky - how many stars visible?

texts:
How would the night sky look like from the Martian surface?

Would there be more stars visible or less (compared to Earth)?

Would they appear brighter/dimmer/same?


texts: What is the temperature of the light that leaves the Sun towards the Earth and does it cool down during it's journey here ? If it doesn't cool down then how come it isn't frying the Earth ? Is it our atmosphere that is preventing it from doing so or does it cool down during it's trip here in space ?


texts:
I need to determine Right Ascension and Declination from Azimuth and Altitude, working in C#. The problem is that the formula for calculating hour angle, for some reason, doesn't work. Here's the code:

        az = az * DEG_TO_RAD;
        alt = alt * DEG_TO_RAD;

        lati = latitude * DEG_TO_RAD;

        // Julian day
        JD = CalculateJDN(year, month, day, h, m, s);

        // Greenwich mean sidereal time
        GMST = CalculateGMST(JD);

        LST = GMST + longitude / 15;

        dec = Math.Asin((Math.Sin(lati) * Math.Sin(alt)) + (Math.Cos(lati) * Math.Cos(alt) * Math.Cos(az)));

        ha = Math.Atan2(Math.Sin(az), (Math.Cos(az) * Math.Sin(lati) + Math.Tan(alt) * Math.Cos(lati)));

        ha = ha * RAD_TO_DEGREE / 15;
        dec = dec * RAD_TO_DEGREE;

        ra = LST - ha;

        // Input data for Mintaka (delta Ori):
        // az = 47.5, alt = -35.3 on 13:57 UTC, 1 Dec 2015
        // latitude = 43.897, longitude = 20.344
        // Required output: dec = -0.19, ra = 5.5
        // Given output:
        // dec = -0.19, ra = 17.5, ha = 2.5

Az and alt are given in degrees, so they are first converted into radians. Functions for calculating Julian day number and GMST are correct, since I've already tested them. Formula for declination is good, but for some reasons formula for hour angle (ha) doesn't work. I don't know where's the error.


texts: Would Europa be an ocean planet if it were in the habitable zone?

texts: If a Europa-like body were in the Sun's habitable zone, let's say in an orbit between Earth and Mars, would the body become and remain a water ocean planet? In the habitable zone, the Sun would warm up and melt Europa's icy surface which will first turn into water vapor because Europa has no atmosphere, but the water vapor might form an atmosphere around Europa (which would contain oxygen as well) and eventually Europa might get a liquid water surface. Would that be possible? And would the atmosphere remain or couldn't it remain due to Europa's low gravity? But what if the Europa-like body had a Mars-like gravity and/or an Earth-like magnetosphere?


texts: Why do in general stars twinkle and planets don't?

texts:
I got an email update on what can be observed this week.

Jupiter looks like a bright yellow-white star, almost as bright as
Mars. Saturn is about 10 moon widths to the left and slightly above,
and is much fainter, but still bright enough to see from Cambridge. In
general, planets can be distinguished by their lack of twinkling,
while stars do twinkle.

Why is that the case that stars twinkle, and planets don't? I am aware of variable stars, but I don't think the email means that, since twinkle usually means much more rapid change than variable stars usually exhibit.


texts: Why does the moon looks like having different filters sometimes?

texts:
Why does the moon look more yellow or more LED-like?
Thanks in advance


texts: How do I obtain the brightness of a star in the night sky?

texts: I am planning to conduct a research which involves observing the brightness of a star. So far, I haven't been able to obtain much information as to how I may go forward with the observation process. I'm willing to buy a telescope and other equipment. What telescopes are ideal for this and what other equipment must I require to obtain the apparent brightness value of the star?


texts:
In this answer I mention that for very low orbits around spherical bodies, the period tends to scale only as the inverse square root of the density, and not the diameter.

For a low orbits where the semi-major axis is close to the radius of the central body, the period is related to the average density of the body and unrelated to it's size.
So a low orbit around a spherical asteroid (which there usually aren't) made of a mixture of rock and iron (which there usually aren't) will be roughly 90 minutes just like LEO (low Earth orbit), even if it's only 1 km in diameter.

I'd like to use an example, but I don't know where to find an asteroid density table, nor even a histogram, that includes something close to 5 g/cm^3.
Question: Are there any known asteroids with average density similar to that of Earth's?
Some example mean densities from Wikipedia (some rocky planets included for good measure):
body      mean density (g/cm^3)

Earth            5.5
Mercury          5.4
Venus            5.2

Mars             3.9
Io               3.5
Vesta            3.4
Moon             3.3
Hygiea           2.8
Pallas           2.7
Ceres            2.1


texts:
I'm making a technological project. The goal is to write a program that gets an image of the nightsky and predicts the hour in which the photo was taken.

I implemented a well-known method using the big dipper, but it's not enough. I don't want to limit my program to only work when the big dipper is in the image.

When I read about right ascension, my gut told me seeing a star in the sky and knowing its right ascension (RA) would help me deduce how many hours ago the sunset happened, though I couldn't explain how.

I'm not comfortable enough with this coordinate system, so I need help answering this question:
Say I konw the location a photo was taken, and I can identify the celestial objects in the sky and get their RA, can I make some calculations to konw/approximate the hour? If so, how?

Thanks in advance!


texts: Can primordial black holes be found orbiting other stars?

texts:
A recent study suggests a that a primordial black hole may be orbiting the sun at and that they can be common near other star systems.

What measurements and equipment can perhaps find BH's near other stars?


texts: If a rogue planet disrupts Earth's orbit slightly to cause a long winter or summer will the Earth's orbit normalize back close its original orbit over time? Could a Planet X or some other elliptical orbit large body revolving around the sun effect Earth's orbit by being inside the inner solar system?


texts: Presenting / printing Right Ascension and Declination values

texts:
Are there any standards or established practices on how to write / represent Right Ascension (RA) and Declination (DEC) values in the sexagesimal format?
I have seen all of the following. E.g. for RA:

02 03 04 (assumed to mean 2 hours, 3 hourly minutes and 4 hourly seconds)
2 3 4 (same as above)
2h 3m 4s (same as above)
2d 3' 6" (assumed to mean 2 degrees, 3 degree minutes and 4 degree seconds)
2d 3m 6s (same as above)
15.33 (assumed to mean 15.33 degrees)
9.5H (assumed to mean 9 hours, 30 hourly minutes and zero hourly seconds)
8d 3.5 (assumed to mean 8 degrees, 3 degree minutes and 30 degree seconds)

Likewise for DEC (even though for DEC when the first component does not have a suffix it is assumed by default to be in degrees, not hours). Does any astronomical association publish guidelines for the printing / presentation of such values or on how software should accept user's input of such values?


texts: The colour of saturn as it appears to the naked eye

texts:
I have started to watch the skies in order to learn stars, constellations planets etc. The few references I checked state that Saturn presents itself to the naked eye as a pale yellow tiny little ball, easy to notice if one knows beforehand its position.

So, using Stellarium I have managed to learn that Saturn is near the Scorpio constellation, just below its claws, which is easy to spot because Antares has distinct red-orange colour.

However, when I first spotted the planet I noticed that it was like a blue ball. I should say it looked like a pale, near white blue or a pale blue, near white -- I can not be more precise than this.

I am spotting it correctly? I was taught that planets do not scintillate like stars. The ball I am talking about certainly did not do it. If I did spot it correctly, I would like to ask if and how often Saturn changes its colours.

p.s. I thought it might be a case of city pollution, however I should say I live in a small mountain village with very few if any air or light pollution.

Many thanks in advance.


texts: Is the expansion of the universe greater than the speed of light?

texts: If the rate of expansion of the universe is increasing , won't it eventually become greater than c? Also, after inflation, did the rate of expansion slow down and then start to accelerate again?


texts: I know that some of them are pulsars and pulsars spin very fast, but do all of the neutron stars spin? I would think that they would because of conservation of momentum, but I'm really just not sure.


texts: How to determine the ellipticity of galaxies in SDSS

texts:
What is the best approach to determine the ellipticity of galaxies in the SDSS DR12. I have read this page. Are those really good methods?

Do flux-weighted second moments (as given in the stokes parameters) really give the correct value for ellipticity?

Also I am not sure what table field they actually refer too (in the Galaxy view) when talking about the method using the Adaptive Moments. For example where can I find the m_rr_cc value for the method described here?

Update

I have calculated the ellipticity of a spiral galaxiy with two different methods using data from SDSS DR7. First I used the method using the stokes parameters and second I used the values for isoA and isoB. Both calculations where done in the r-band.

The data can be obtained with the following CAS Query:

SELECT
    g.objid as objId,
    /*  stoke parameters*/
    q_r,u_r,
     /*  iso_a, iso_b */
    isoA_r,isoB_r
FROM Galaxy AS g
WHERE
    g.objid = 587722982832013381

yielding the result

objId: 587722982832013381
q_r : -0.1206308
u_r: 0.002988584
isoA_r: 169.3949
isoB_r: 84.78848

The ellipticity by stoke parameters is given by

$$
e  = 1 - \frac{b}{a} = 1 - \frac{1 - \sqrt{Q^2 + U^2}}{1 + \sqrt{Q^2 + U^2}}.
$$

The ellipticity from isoA and isoB is very given by

$$
e  = 1 - \frac{isoB}{isoA}.
$$

But I get completely different results when I use isoA and isoB or the stoke parameters. I get:

ellipticity from stoke parameters: 0.2153498356
ellipticity from 1-(isoA/isoB): 0.4994626166

The results can be reproduced with the following python code:

import math

def ellipticityStokes(q, u):
    e = 1 - ((1-math.sqrt((q**2) + (u**2)))/(1+math.sqrt((q**2) + (u**2))))
    return e

def ellipticityNormal(a, b):
    e = 1 - (b/a)
    return e

q = -0.1206308
u = 0.002988584

isoA = 169.3949
isoB = 84.78848

print(str(ellipticityStokes(q,u))) #0.2153498356239003
print(str(ellipticityNormal(isoA,isoB))) #0.4994626166431221

Looking at the image

(and compare with this website from Buta) I would say the value 0.4994626166 (from isoA and isoB) makes more sense. The value calculated from the stokes parameters is just wrong I think.

What is the mistake here? I would expect both calculations to yield similar results.

However for newer data releases isoA and isoB are not available any more because they seem not to trust those value? What should I do with newer data releases as DR12?


texts: Converting Invariable plane to J2000 ecliptic

texts: I've been following the answer given by Mike G here: How to calculate the orientation of planets at current epoch to get planets to have the correct orientation in my program, but all the angles are in the Invariable plane, how is that converted to the J2000 ecliptic plane? I've been stuck at this for hours and it makes my head hurt, any help would very much be appreciated!


texts: When will Callisto be in orbital resonance with the rest of Jupiter's big moons?

texts:
The four Gallilean moons of Jupiter (from innermost) are Io, Europa, Ganymede, and Callisto.  Io, Europa, and Ganymede are in a 1:2:4 orbital resonance. Callisto's orbital period is 16.689 days, which is not much more than twice Ganymede's period of 7.1546 days.

If Jupiter's orbit around the Sun was stable, when could we expect Callisto to come into a 1:2:4:8 orbital resonance with the Jupiter's other Gallilean moons?
Related: Does anyone know why three of Jupiter's largest moons orbit in 1:2:4 resonance?


texts: Vertical speed vector at which the sun travels to and from the galactic equator

texts: What is the speed of progression of the sun toward and away from the galactic equator during its orbit?


texts: Why doesn't the moon always follow the same path? Or why aren't the moon's apoapsis and periapsis fixed?

texts: I have seen many times that the moon doesn't follow the same path. Sometimes the moon gets very close to earth which is shown in the news. If the periapsis of the moon is soo close then why doesn't a super moon occur every 27 days? And if the moon is inclined at 5.1° so how can more than 2 eclipses occur in one year?


texts: Could any known, living organisms on Earth survive on Mars?

texts:
No life has been discovered outside of Earth (yet?), but do we know if anything that would be considered "living" on Earth could conquer Mars? (or maybe Venus?)

With the Mars One project on the way, I was wondering if it was possible to transplant some of Earth's life to Mars, and if something could survive there (naturally).

Many kinds of life are based on air and sun. Animals have to breathe oxygen, plants need the sun, and both need water. But there are many other kinds of life on Earth, like:

Very deep seawater life that lives under high pressure and without sunlight,
extremophile organisms that live in very hot water,
weird "arsenic life" which was debunked as being fully arsenic-based, but turned out to be something different...

Have there been any theories or studies about unusual forms of life on Earth that might survive on Mars?


texts: Strange speck of light in the picture sequence of the approach to 2014 Mu69 (Ultima Thule)

texts:
In the picture sequence which was taken by New Horizons during the approach to Ultima Thule on the 3rd of Dec there can be seen a speck of light in the lower left corner, not as bright as 2014 MU69 but clearly visible.

Source: Here (German) or here (English), NASA / Johns Hopkins Applied Physics Laboratory / Southwest Research Laboratory / Henry Throop

Is there any theory what may have caused this signal? A particle from the probe itself, coincidentally passing in front of the lens? A variable star? A small object in the right distance and angle to be glimpsed upon by New Horizons? I think the latter would be an astronomically improbable event...

Here are some single frames of that image sequence, the speck is clearly visible on the 3rd of December.


texts: How does one go about naming a lunar crater?

texts: Suppose I discover an uncatalogued crater on the lunar surface, and decide to name it. How would I submit my proposed name to the IAU?


texts: Do ASKAP and ALMA have "fast dump" interferometric modes? Can they see and perhaps report Fast Radio Bursts in real time?

texts:
Chatterjee et al 2017 The direct localization of a fast radio burst and its host nicely shows a VLA detection of a repeating FRB in 5 millisecond steps nicely demonstrating the dispersion slope matching that of FRB 121102 and when de-dispersed providing a precise epoch for the particular event that could be potentially matched to other simultaneous observations while simultaneously providing the spatial resolution of an interferometric radio telescope array.

VLA fast-dump observations.
The VLA fast-sampled interferometric data were recorded with 5 ms integration time, 256 channels, and bandwidth 1024 MHz centred at 3 GHz.

Kumar et al. 2019 Faint Repetitions from a Bright Fast Radio Burst Source show ASKAP measurements of repeating FRB 171019 with 2.62 and 1.26 millisecond resolution. However the array was operated in fly's eye mode with each dish pointed in a different direction, so if I understand correctly, interferometric resolution from the array was not available.
I haven't found any reports of or references for ALMA FRB detections.
Questions:

Do ASKAP and/or ALMA have "fast dump" interferometric modes? Or do they have at least some way to extract dispersion of transient events at the millisecond level?
Can either see and perhaps report Fast Radio Bursts in real or near-real time?

Figure 1 VLA detection of FRB 121102. (a) A 5-ms dispersion-corrected dirty image shows a burst from FRB 121102 at MJD 57633.67986367 (2016 Sep 02). The approximate localization uncertainty from previous Arecibo detections (3' beam FWHM) is shown with overlapping circles. (b) A zoomed in portion of the above image, de-convolved and re-centered on the detection, showing the ~0.1" localization of the burst. (c) Time frequency data extracted from phased VLA visibilities at the burst location shows the $\nu^{-2}$ dispersive sweep of the burst. The solid black lines illustrate the expected sweep for
DM = 558 pc cm^−3. The de-dispersed lightcurve and spectra are projected to the upper
and right panels, respectively.

Figure 2. Dynamic spectra for both repeat bursts detected at GBT and ASKAP FRB 171019 dedispersed at their optimal DM. From the left: repeat burst 1 (resolution = 1.31 ms), repeat burst 2 (resolution = 2.62 ms), and ASKAP FRB 171019 (resolution = 1.26 ms). For each burst, the top panel shows the flux density averaged over frequency channels.


texts: Stellar catalogues stars in specific sky regions – without downloading the catalogs

texts:
I’m interested, to give a scientific realism to a project I’m working on, in finding a picture of all stars belonging to a star catalogue such as Tycho 2 or Hipparcos for some very specific sky regions.

Since I have little time available, I’m wondering whether there’s a quicker way (maybe online?) than downloading the whole catalog and browsing through it via some dedicated software.

Thank you

D.


texts: Were parts of the Universe deflating during Inflation?

texts:
I was reading about the history of the early universe in Carroll & Ostlie and specifically looking at Inflation, which, as I understand, occurred because our [observable] part of the universe entered a false vacuum state containing negative pressures, thus fueling expansion. (Carroll & Ostlie state the opposite, but as per the discussion below, that appears to be incorrect).

Does that mean that there are other parts of the Universe (outside of our horizon) that experienced deflation, as inflationary parts pressed against them? Would there be boundaries between separate parts of the larger universe where inflationary parts encounter one another? Any thoughts on what those parts of the Universe are like, such as containing their own CMB that's NOT close to uniform, or where there is a much higher density of matter?


texts: It is known that spacetime is curved,so I am wandering to know if its possible to look into space and we see earth (light from earth long long ago). Did I understood spacetime correctly and if its possible then can some one after million years can see dinosaurs by looking into space?


texts:
Let Line A be the projection of the axis of Earth's rotation onto the plane of the eliptic.  Let Line B the line connecting the center of the Earth and center of the Sun.

At what times during the year is Line A perpendicular to Line B?


texts: Is it possible to revive the Mars geodynamo?

texts:
I’ve done a bit of reading and have found multiple theories suggesting how the Mars geodynamo stopped fully working.

This site suggests that one possibility could be volcanic activity ejecting water and other necessary elements from the mantle significantly slowed the natural convection process.

Where as this site says that it also could have been massive asteroids colliding with the surface, heating the planet up to temperatures that would disrupt convection.

No one is quite certain what happened, all that is known is Mars doesn’t have much of a magnetic field at this point.

Today I saw that there’s an idea to create an artificial field that’ll act in place of a geodynamo’s naturally generated one.

My main concern for this is that the units creating the artificial field could be destroyed and the entire planet would become unstable afterwards.

It would seem if the magnetic field is supported by the planet itself, it would offer a higher degree of stability and less involvement for humans in the long run.

What’s the possibility for ‘restarting’ the Mars geodynamo or perhaps ramping it up enough to support a strong enough field? And if so, how would we be able to do it?


texts: Would we detect a spacecraft before it landed on Earth?

texts:
We have satellites and telescopes looking outward and inward to the earth. Would any of these detect an extraterrestrial spacecraft before it landed, or in other words, would we know a spacecraft was approaching before it did (assuming its going at some reasonably detectable speed in our local area)?
Let's assume it is Saturn V like wrt detectability.


texts: What is the nature of bright spots found on Uranus?

texts:
The following text is from space.com which was written during the time of discovery of the first dark spot on Uranus:

During the past decade, many bright spots have been seen on Uranus in
both red and near-infrared filters. But this is the first dark spot
ever seen on the planet. A team led by Lawrence Sromovsky of the
University of Wisconsin and including Kathy Rages of the SETI Institute,
Heidi Hammel of the Space Science Institute (Boulder, CO), andPatrick
Fry of U. Wisconsin, observed the dark spot on Aug. 23 using the
Hubble Space Telescope (HST).

What was the nature of the bright spots? How were they formed? Was it some form of storm or vortex? I couldn't find any information anywhere regarding this.


texts: How can satellites be safe in the atmosphere when there are so many asteroids coming in?

texts:
How  can artificial satellites be safe in the atmosphere when there are hundreds of tons of dust and asteroids coming into earth's atmosphere everyday?

What is an orbit of an artificial satellite?
At what approximate distance (or which orbit) from artificial satellites do these asteroids, dust, rocks annihilate?


texts: Solar Noon: meridian crossing time versus time of maximum elevation

texts:
According to the first paragraph of the Noon Wikipedia page, solar noon is the moment when the Sun crosses the meridian and is at its highest elevation in the sky. The wording there suggests that there is an exact identity between the solar meridian crossing time and the solar maximum elevation time on a given day. However, later in same article in the Solar Noon section it states that,

  Solar noon is the moment when the Sun transits the celestial meridian – roughly the time when it is highest above the horizon on that day.

(Emphasis mine)

The use of the word "roughly" really surprised me. I was strongly under the impression that these times were necessarily equal for sub-polar regions. Am I wrong and missing something, or is the wiki article just poorly worded?


texts: XKCD 1944 claims that there is "more gold in the sun than water in the oceans". Is this really true?


texts: Why are Mars northern/southern hemisphere altitudes so different?

texts:
I'm looking at the Mars topography map:

original link

...and I can't shake the impression that someone just messed up the placement of the center point of the planet, shifting it about 8km north from where it should be. If the center point was ~8km further south, the north and south altitudes would be roughly the same. Moreover, it's even hard to argue about placement of equator, as the northern pole is about 16km closer to the equatorial plane than the southern - due to the altitude difference. Move the equator and it all evens out.

It's fairly hard to believe such a mistake to have persisted so long, so... is there any deeper reason behind this strong asymmetry of the planet, other than just a topographical snafu?


texts:
I have read a number of articles about Coronal Mass Ejections (CME) and solar flares and I’m trying to establish how directional the radiation from them is.
I am aware that radiation from these solar events does not travel directly outward from the direction of the sun but follows magnetic lines of force and may be subject to eddies and other other effects that modify the direction of travel.
So my question is: What does the graph of average radiation intensity v radial distribution look like for a point in deep space (radiation intensity v degrees bearing from the line of maximum intensity) for a passing solar flare or CME? For the purpose of this question, deep Space is the region between the orbits of Venus and Mars


texts: Binocular highlights from Tasmania next few weeks?

texts:
My friends are visiting southern Australia and Tasmania for the next few weeks.

I am lobbying them to bring my Nikon 8x42 binoculars so they can appreciate the Milky Way and possibly see a few other things.

What I need is:

What parts of the Milky way will be most spectacular in binoculars at night at about 40° South latitude around this time of year?
Anything else? I've never stargazed in the Southern hemisphere so I have no idea what to point them towards.

I can use online star maps (e.g. in-the-sky.org) so I can give them directions how to find things if it's not hard, but I don't have any idea what "things" there are.


texts: If galaxies are moving away from each other then why are the Milky Way and Andromeda galaxy coming towards each other?

texts:
The Andromeda Galaxy is approaching the Milky Way at about 684000 mi/hours, making it one of the few blueshifted galaxies. The Andromeda Galaxy and the Milky Way are thus expected to collide in about 3.75 or 4.5 billion years.

Why are some galaxies moving away and why are our galaxy and Andromeda coming towards each other?


texts: Why does Saturn have a more prominent equatorial bulge and higher flattening ratio than Jupiter despite rotating slower?

texts:
It is my understanding that a planet's equatorial bulge is caused by the centrifugal force produced by its rotation, and the faster a planet rotates the bigger the bulge and flattening ratio of a planet is.

Jupiter's rotational period is 9.925 hours while Saturn's is 10.56 hours. However, Saturn not only has a higher flattening ratio than Jupiter, but also has a bigger equatorial bulge (11,801 km vs. 9,276 km) despite rotating slower and being smaller. Am I missing something?


texts: Is there any real chance of getting hit with a meteorite if we build a base on the moon?

texts:
I've been reading an article today on how the European Space Agency (ESA) has an interest in building a space village on the moon which will be 3D printed and assembled by robots. Eventually people will start to go there for long periods of time (presumably).

I always think to myself when hearing such news or watching a sci-fi movie, isn't there a real chance that it will get hit by a meteorite?

Resource:
http://www.iflscience.com/space/esa-build-moon-village-2030

UPDATE

Here's a video of their plan to build a moon village as they call it:
http://www.iflscience.com/space/esa-reveal-their-plans-build-moon-village-20-years-time

UPDATE #2

Something interesting to see :) http://www.iflscience.com/space/space-debris-has-chipped-one-isss-windows


texts: Orbital elements: Difference between longitude of perihelion and argument of perifocus

texts: I am learning orbital elements and one thing isn't clear to me. When I look at the Horizon's ephemeris data for Mars, this gives me argument of perifocus equal to roughly 286.53 degrees on epoch J2000. When I look up its longitude of perihelion for the same epoch here, I get roughly 336.04 degrees. I thought these two parameters are the same thing. What is the difference between them? Why are the two numbers not the same?


texts: Why is the moon drifting? Shouldn't orbital decay bring it closer?

texts:
I noted that the moon drifts away from Earth a few centimeters each year.

However, I'm thinking that the emission of gravitational waves would deter such thing and cause the exact opposite. Furthermore, the orbital decay due to tidal forces should also slow the mon down, which allows the Earth to pull and being the moon closer. What mechanism is working to drag the moon further away from Earth?


texts: What did I photograph around 6 AM on April 27th, 2021? Supermoon plus comet?

texts:
Facing SW just before sunrise on April 27, 2021 in Central Florida:
The timestamps on the pics start at 6:23 end at 6:27.  It was still visible and breaking up like a post launch trail that I would see in the east.  By the size, from beginning to end, looks like the direction was from/could be described as, from New Orleans toward Ft. Myers crossing between the moon and Gulf of Mexico.  Because its small early Northwest of moon and larger late south of moon.


texts: What were the challenges for the ancients to observe the orbit of the Moon (instead of Mars)?

texts:
Astrophysics can be said to have been founded by Johannes Kepler around the year 1600. He based his break-through science on data of the position of Mars in the sky and disproved the ancient ideas about circular orbits and epicycles.

But why wasn't this done far earlier, by using observations of the Moon? Wasn't it pretty obvious to a careful astrologer a thousand years ago, that the Moon does not have a circular orbit and does not describe epi-cycles? It is the easiest celestial object to observe, visible both night and day. Moon calendars may have been designed tens of thousands of years ago, there's no lack of observational data. Kepler instead used a few oppositions of Mars which take place only once every two+ years. Since the Moon is the one object which does orbit Earth, in a geocentric world view it should've been the perfect test of circular and epi-cyclical theories about its orbit. Its nearness causes a daily parallax between moonrise and moonset, but that wouldn't be beyond a genius like Kepler or many mathematical astrologers before him.

What made the orbit of the Moon difficult for the ancients to understand?


texts: Get visible galactic longitudes in astropy

texts:
I would like to know which part of the Milky Way is currently up. Preferably using astropy. The ingredients I have are the current time, and my current position on earth. How would I use these to get the minimal and maximal galactic longitude currently up?

(I know how to convert from Alt-Az to Galactic coordinates, but I don't know at which azimuth the galactic plane crosses the horizon at altitude=0.)


texts: Is there a legend for these 88 HST images?

texts:
Is there a legend for these 88 Hubble Space Telescope images?

I have a 6000px x 4800 px version of this image (reduced & rotated to 480x600 here) that I use for an image slide show.  I would like to add the description of each image into the slide show software.

On this system the file name is HubbleGallery.jpg but I suspect I coined that title (it was a long time ago it was downloaded).  The original image is 5,150,779 bytes in size.

Searching on the smaller, rotated version of the image points to pages like Astronomy Printshop, but there is nothing closely related to NASA in the first pages of the search, and the pages listed did not have much detail (certainly no legend).

It might possible to search on the clipped, individual images, but I was hoping to avoid having to do that 88 times.


texts: Could some bacteria theoretically evolve to survive in space?

texts: There is no edge to the atmosphere, and therefor I expect there would be a gradual reduction of concentrations of bacteria as we ascend into space. Logically anaerobic bacteria should be able to obtain its energy from the sun and nutrients from whatever scarce but available organic floating materials. Cosmic rays and high energy particles could damage DNA, but there might be someway life could protect itself against them. Could it be that bacteria is evolving/ has already evolved at the edge of the atmosphere to live in space?


texts: Starlight: are the rays that we see here on Earth parallel?

texts:
Are the rays of light emitted from stars that are perceived by an eye here on Earth parallel?
Do they travel in a straight line from the star to the eye, never crossing, and equidistant?
Do they wiggle around and cross as they move through space?
Do the rays meet at a point on the retina of the eye?
Assuming that a star is pretty far away, it seems reasonable to think that they've traveled zillions of miles without being parallel.


texts: Locating a star cluster on a Hertzsprung-Russell diagram with other color index

texts:
Recently I took pictures of the NGC 884 cluster in the B and I bands and selected some 30-what stars from them. I've reduced the data to a colour-magnitude diagram (absolute magnitude in the I band $M_I$ vs. (B-I) colour index). I am now asked to designate where the stars I've selected from this cluster are located on the Hertzsprung-Russell diagram and the approximate age of the stars.

My problem is the following: any HR diagram that I can find is either expressed in effective temperature instead of colour index, or is in the colour index (B-V). Also I can only seem to find empirical formulas for the effective temperature that use the (B-V) colour index, not the (B-I) one.

Does anyone know where to find an HR diagram that uses the (B-I) colour index?


texts: Can one detect from earth that angular momenta of its axial rotation and its orbital rotation are "almost parallel"?

texts:
I mean that the angle between these angular momenta is acute as opposed to obtuse (23.5 and not 180-23.5), so that the rotations are "roughly in the same direction".

Related but distinct question -- when was this actually discovered?


texts: Giant variation of the proposed eLISA mission using reflectors on Earth and the Moon possible?

texts: I was thinking about the proposed ESA mission eLISA, which is essentially a space version of the LIGO experiment, and it occurred to me that trailing three satellites behind the Earth's orbit seemed excessively complicated in comparison to using a reflector on the ground and another on the moon (if I am not mistaken, there is even already a mirror on the moon, from the Lunar Laser Ranging experiment) and a single satellite. Is there not a geosynchronous orbit with a line of sight to the moon at all times? It seems to me the added range would provide better sensitivity. Provided you know the exact distance to the reflector, you can calculate individual frequencies for the Earth and Moon lasers, downconvert the faster frequency through a PLL of sorts, and still use the resulting data in an interferometry analysis. Is there something major I am missing here that would make this arrangement more difficult than the proposed eLISA mission? It seems to shift a lot of the physical risk and cost of the mission to computational costs, which by comparison are much, much cheaper.


texts: In the calculation of GMST, what are these constants?

texts:
GMST = 6.697374558 + 0.06570982441908 D0 + 1.00273790935 H + 0.000026 T2

From the GMST calculation on the USNO website (and many other places) we encounter these constants:

6.697374558
0.06570982441908
1.00273790935

Can someone enlighten me as to what they represent?


texts:
One of the simplest versions of Newton's equations of motion for the Sun, Earth and Moon can be obtained by making the approximation that the three bodies are perfect spheres. In this approximation, the pair potential between body i and j is  $$\frac{-G m_i m_j}{ r_{ij}},$$ where $r_{ij}$ is the distance between the bodies: one can solve the equations numerically and get the orbits.

This simple model does not include multiple, additional factors, such as

the fact that the Earth is not perfectly spherical (equatorial bulge),
Earth's tides,
the influence of other celestial bodies,

and others.

Amongst all these factors, what is the dominant one as for predicting the orbit of the Earth? In other words, what is the leading factor that should be included in the simple model above in order make its predictions for the Earth's orbit closer to the observations?


texts: Are we looking for brown dwarfs where the dark matter has to be?

texts:
We have been repeatedly assured that their ain't enough brown dwarfs to account for all the dark matter in our galaxy.

My question is have we been looking in the right places?

Or in more detail. Where exactly does computer modelling put the missing mass?

I would expect the bulk of it to be on the galaxy's plain and on the edge. And if I am not mistaken there is too much junk in the way to look.

Further I can't see any reason why the dark matter won't be unevenly distributed in clumps just like everything else.

So, given the above an extrapolation from what we have detected will be way low if it assumes an even distribution in all directions, and horribly low if the LMG and GMG happen to be between clumps.


texts: I recently bought a telescope, but it doesn't have a very clear image.  Where can I buy a better mirror?


texts: Does every object in the Universe have gravity? Space has no gravity, why?

texts: My science teacher told me that every object in Universe has gravity but space is a part of Universe too, so,  why does the space have no gravity?


texts: Pair together light curve and radial velocity data of specified star

texts:
I would like to create a web application that works with light curves and radial velocities of stars with exoplanets. I found a NASA bulk data download with both light curves and radial velocities (it's exactly what I'm looking for). However, I don't know how to pair together the light curve and radial velocity of a single star (without downloading the whole dataset).

For example, using the script below I can download the light curve of KIC 10666592, where there is 1 exoplanet:

wget -O 'kplr010666592-2009131110544_slc.fits' 'http://exoplanetarchive.ipac.caltech.edu:80/data/ETSS//Kepler/005/755/19/kplr010666592-2009131110544_slc.fits' -a search_33681064.log

Now, how can I download radial velocity data for this specific star? Scripts for radial velocity look like (there is no KIC in URL):

wget -O UID_0000522_RVC_001.tbl http://exoplanetarchive.ipac.caltech.edu:80/data/ExoData/0000/0000522/data/UID_0000522_RVC_001.tbl -a RADIAL.log

Is there any way to connect KIC (Kepler input catalog) and radial velocity UID?


texts: At 6:30pm central time in the USA I saw a rapidly twinkling red blue and white star in the sky. It was about south east and I was really confused. I looked it up it might be Sirius but I'm not sure. I know it's not an airplane cause it hasn't moved in 20 minutes. Does anyone know?


texts:
During its formation approximately 4.5 bya, Jupiter passed through what is now the asteroid belt,gravitationally deflecting some spacewards and some sunwards.
Logically, Jupiter, due to its massive gravity, must have swallowed up a fair portion as well.

Is there any way to calculate how much rock Jupiter contains? Have any estimates been made?


texts: Why does the Hertzsprung–Russell diagram's x-axis go from large temperatures to lower?

texts:
In my textbook, the H–R diagram’s y-axis is $\log(L/L_{\odot})$ and values are higher as we go higher on the scale, but the x-axis is $\log(T_\text{eff})$ and gets smaller as we proceed to the right.

This confuses me. Why not let the x-axis go from lower values to higher values? This will also help visualising the “linear” relation between the luminosity and the temperature of a star in the main sequence.


texts: Are the compact objects in supernova remnants isolated neutron stars?

texts:
It seems all the central compact objects correlated with supernova remnant(SNRs) are isolated, not in binaries, right?

I find only one exception. A source is claimed to be a compact binary which correlates with SNR G308.3-1.4.ads link

My question is, generally, are the compact objects in SNR always isolated?
And observationally, are the compact objects in SNRs neutron stars?


texts: In stellar aberration, is there any prism effect, chromatic aberration?


texts: 'Little h' usage in cosmological simulations

texts:
I am running a cosmological simulation and am having some trouble putting things into code units. The physical distance units in my simulation are in terms of $\text{Mpc/h}$, where $h$ is the dimensionless Hubble parameter. This makes enough sense because, as noted elsewhere, simulations are often scale-free so it makes sense to factor out the $h$ dependence and make it explicit. This unit convention is causing me some confusion however. In one calculation I have to do during the simulation, I essentially (ignoring context which I can provide later) have to multiply the speed of light $c$ by an inverse distance $1/x_0$ which is given in units of $\text{Mpc/h}$.

In order to properly have the units cancel, I first put $c$ in units of $\text{Mpc/s}$ to get
$$
9.716 \times10^{-15} \text{Mpc/s}
$$
However, should I know factor out the $h$ dependence? These seems strange to me because in my mind, the value of the speed of light should not depend on the underlying cosmology I have simulated. On the other hand, I feel that I should not cancel units of $\text{Mpc}$ with units of $\text{Mpc/h}$. To make things concrete, let's assume I have a value of $h=.7$. Should I then take the quantity above and multiply it by $.7$ to yield
$$
6.802 \times 10^{-15} \text{(Mpc/h)/s}
$$

and use that result in my calculations? I think this situation confuses me because it doesn't involve measurements, where it is clear how $h$ can enter, and it involves a constant of nature, which should be independent of the assumed cosmology.

Let me know if more info is needed.


texts: What is the mass limit in a stellar accretion disc?

texts: I became curious about the maximum mass in a star's accretion disc while watching an episode of Star Trek involving a Dyson Sphere. I wondered if some maximum amount of stellar material would limit natural and artificial structures around any system of one or more stars. What affects these limits? Is there a logarithmic/linear/exponential correlation between stellar mass and maximum accretion mass?


texts: Are objects in the universe moving away from each other at the same acceleration?

texts:
This is a follow up question to Does the universe expand at the same rate everywhere in the universe?.

If the universe is expanding, then it would seem necessary for each object (ie galaxy) to be accelerating away from every other object at the same rate of acceleration which is constant (or not?). If that is true, what is the acceleration?

In other words, relative to the Milky Way, does it seem that all the other galaxies are moving directly away from us at the same rate of acceleration? If so, is it possible for us to prove that for any other galaxy that we know, the same observation would be true, were we able to view the universe from that galaxy?


texts: Does the event horizon of a black hole increase or decrease by adding mass?

texts: So a black hole is a something that has enormous gravity, therefore mass accelerates faster towards it. But if the black hole double  it's mass, will it's event horizon increase in length , or will it decrease?


texts:
I know there are a number of parameters that determine the occurrence of a solar or lunar eclipse. The number should be 18; 6 degrees of freedom for 3 rigid bodies. But can't figure out why eclipses are not repeated.

When we have a night with a full moon, the next night we again have a close-to-full moon, so it can be considered a distribution over several days. What prevents the same happening for eclipses? Is it possible to have two semi-eclipses in two consecutive days? If not, why does such a big difference occur over just a day?

Thanks,


texts: Is the CMB the photons that were created at the birth of the atom?

texts: Is the CMB that we see the same, unchanged energy from this moment? Does the radiation of the CMB exist as Photons and are we only witnessing the photons that have not been absorbed or destroyed? Will there be a time we can no longer witness the CMB because it has all been absorbed? How does red-shift factor in to this?


texts: Is there a way to calculate the expected number density of Dark Matter Halos above a given mass, in a certain redshift range, and in a certain area?


texts:
This thorough answer to How long does lunar opposition surge last? Are there measurements of the full Moon getting suddenly brighter? details observations of lunar opposition surge by the Clementine and Lunar Reconnaissance orbiter.
But we don't have to go to lunar orbit to see the sunlit Moon, we can observe the lunar disk right here on Earth.
Question: Has lunar opposition surge ever been observed from Earth? From Earth orbit?


texts: Can I find exoplanets without a telescope?

texts: I would like to know please whether or not I can look for exoplanets without a telescope.


texts: Do other G-type stars follow an 11-year cycle of activity?

texts:
Our Sun follows an 11-year cycle of low-to-high activity. During high activity, there are much more sunspots and much higher chance of flares and other disruptive behavior.

Can we observe the activity of other stars? I'm particularly interested in other G-types like the Sun. Do they also follow an 11-year cycle?


texts: Where can I find a set of data of the initial conditions of our solar system?

texts:
As the title suggests, I'm in need of a set of data of our solar system. Similar to this http://bima.astro.umd.edu/nemo/archive/#iau25, but more specifically, the Dubinsky Milky Way-Andromeda data.

I'm creating a n-body simulation for school and can't seem the find any initial particle conditions that I could use to simulate our solar system in the software I'm developing. I need initial positions, velocity and mass.

Any idea where I could find this?


texts: Seeing Azha (Eta Eridani) in Northern Hemisphere

texts:
When I use Stellarium, I am unable to see Azha in London or Atlanta, Georgia.  However, it is possible to see Azha in Tokyo and Auckland.

I am not changing the time, only the location.  I presume that my time is converted to their time.  So for example, if my time is 11:30 (London) then when I select Tokyo, I should see what the sky is like at 11:30 Tokyo time.

I can see Azha in Auckland too.  I would've thought the ability to see a star is based on N/S hemisphere not E/W hemisphere.  Is it right I should be able to see Azha in the Eastern Hemisphere but in the West or am I using Stellarium incorrectly?

I am asking because of the Eta Eridanids. They might be an obscure or a disappointing meteor shower. The reason for such differing locations was to see where in the world it's possible to see them.


texts: How to create synthetic test images of stars?

texts: Is there any python/IDL code available to create synthetic test images of stars with and without background noise?


texts: What phenomena was this video from SOHO actually showing?

texts:
My friend showed me a video of a CME that looked as if it was swirling into a gigantic circular "spaceship" or "UFO" and he explained it as "an alien ship potentially refueling". I did a bit of research and I know assumed the images he was showing me were from SETI SOHO and they were yellow, meaning it was obviously only a single or a couple wavelengths of light shown (possibly UV?).

https://youtu.be/YnzZLNsSGyY

disclaimer: this clip is overly-liberal in its subtitles...

If yoy habe the original source that would be awesome.

Making a total BLIND guess- I'd say the plasma was swirling into the filament of the CME before it reached a critical mass to be pushed away from the sun? Once departed from the energy of the sun under certain conditions it would no longer show because it wouldn't have enough energy to emit the correct wavelength of light?

Am I even remotely correct? Obviously the space ship explanation has no merit- it's just from some dude. Hoping to get a clarification on the video, I do not believe it is a "UFO refueling" heh. Im not a conspiracy nut, and neither is my bud- so we're looking for a science answer :).


texts:
Is a Low Mass Black Hole also called a Stellar Mass Black Hole?
Can Low Mass BH be also called Primordial BH?

(If low mass BH are Stellar Mass BH-What is their size in terms of the mass of the sun?)


texts: How can I see planets with my telescope?

texts: I have bought a Celestron Astromaster 130 telescope and I am relatively new to astronomy, when I tried to view Jupiter a few months ago I could not make out any details. It was just a white orb. Any help with getting clearer images and any advice on viewing. I live on a main road BTW and that's where I was viewing from.


texts: What are the current accepted theories of the formation of the Uranian moon Miranda?

texts:
Miranda, a moon of Uranus is unique in that it has a very fractured surface

Source: University of Oregon

The surface is said to be jagged and fractured, with comparatively large disjointed cliffs and great faultlines.

What are the current accepted theories for the formation of such a strange world?

Please include authoritive links in any reply


texts: It is said that when our solar system passes through the dark rift of galaxy (what is it exactly?), a phenomenon named 'Galactic Eclipse' happens, when our solar system witnesses 3 days of darkness. Is it possible even in this case that there would be no light in the night sky, as there are many stars in the night sky. (don't consider city lights and other artificial human interference)


texts: How to calculate the various properties of a star?

texts:
I am wanting to plot a velocity profile (a plot of velocity against the star's distance from the galactic core) from the Gaia DR2, but so far my efforts have been disappointing.

The information I have for each star are the declination ($\delta$), right ascension ($\alpha$), radial velocity ($v_r$), parallax ($\theta_\text{parallax}$) and proper motion ($\mu$) (ra and dec).

I tried to calculate the star's distance from the galactic core using the cosine rule:

$$ d = \frac{1000}{\theta_{\text{parallax}}}$$
$$\theta = \arccos{[\sin{\delta_\text{star}}\sin{\delta_\text{core}} + \cos{\delta_\text{star}}\cos{\delta_\text{core}}\cos{(\alpha_\text{star}-\alpha_\text{core})}]}$$
$$ r = \sqrt{d_\text{core}^2+ d^2 - 2d \times d_\text{core} \times \cos{\theta}} $$

Where $d$ is the distance from the Sun to the star. $d_\text{core}$ is the distance from the Sun to the galactic core. $\theta$ is the angular separation of the star and the galactic core. $r$ is the distance from the star to the core.

And the star's speed using the equations:

$$\mu = \sqrt{\mu_\text{dec}^2 + \mu_\text{ra}^2}$$
$$ v_t = 4.7 \mu d $$
$$ v = \sqrt{v_r^2 + v_t^2} $$

But the plot doesn't show any kind of trend (just a kind of blob). Have I calculated correctly and, if not, how could I calculate the tangential velocities and radius from the galactic core?

Basically, I want to make the kind of plot that helps us identify dark matter in galaxies.


texts: How spaghettification is possible at the Event Horizon of a supermassive black hole?

texts: if gravity is too strong then it will break a object apart as gravity is strong enough to break the chemical composition of object why we consider "Spaghettification" relevant in this case ?


texts:
I've read several articles and watched some videos on the HR diagram, but no-one seems to mention the effect of redshift on the color of a star. Is there some calibration step that needs to be applied when looking up the Luminosity for a star that you've observed the color of?
For instance, if I observe a star a being a certain color then using the x-axis on the HR diagram I can find that observation's color and find a corresponding location in the HR diagram. However if the star I'm observing is redshifted the color I've observed is not the actual color of that star.
I'm super-new at reading the HR diagram but it really fascinates me and I cannot find why redshift isn't mentioned in relation to it.
Edit: it's not answered by the suggested
Relationship between photometric colour and redshift
as my question isn't so much about about spectroscopy or the types of redshift but simply if the HR diagram applies to far away stars or not.


texts: Why all the photos from 67p are black and white?

texts: I was wondering why every picture we saw on internet about Rosetta's landing on 67p just black and white ? Is there something i should know ?


texts: Retrogradation movement of planet Mars relatively from Earth by Copernic

texts:
I  have a simple question : on the following figure:

I don't understand on the right figure why there is a progressive shift on the right when we start from step 1) to step 9). I guess there is an angle between the rotation plane of Mars and the rotation plane of Earth. Otherwise, we could'nt see clearly the recessing movement if the 2 planes were identical, could we ? We would just draw in the sky a simple line which would be the projection of the curve (on right figure) on a single Oy axis.
Anyone could explain me if this difference in two rotation planes is the cause of the shape of this curve (which is also due to the relative position of Mars from Earth) ?
Any help is welcome.


texts: Why is $g$ tied to the oscillator strength $f$ in $\log{gf}_{\odot}$

texts: The $\log{gf}$ value of an element in a star, where $f$ is the oscillator strength, or probability of transition in an atom, is a scientifically pursued quantity with relation to the model atmosphere of the star. Why is the oscillator strength tied to $g$? And what is the motivation for including this quantity in a stellar model?


texts: If an orbit is shifting due to orbital precession, is it still a Keplerian orbit?

texts: I was thinking about orbits a few days ago, and realized that orbits shift/precess naturally. Given that a two-body problem with a star and a planet, if the planet has an eccentric orbit that precesses, would we still call it a Keplerian orbit?


texts: Is it possible for a person to not see the new moon at different places on earth?

texts:
It is known that theoretically we see the same moon phase everywhere on the earth, but practically I see that people are unable to observe the 0.8% waxing crescent at different places on earth. This has some grave consequences as in some cultures like Jewish,Muslim and hindu moon sighting can mark beginnings of festive months. This link claims that different countries have different eid beginnings:

  In India, Muslims will celebrate the festival on Monday or Tuesday, depending on the moon's sighting. In Pakistan, Eid will be celebrated on Tuesday as there are no chances of moon to be sighted on 27 July, The News Tribe reported.
  In the United Kingdom, Eid al-Fitr is likely to be celebrated on 29 July, according to timeanddate.com.
  In the United States, Muslims will mark the beginning of Shawwal on 28 July, the Fiqh Council of North America, an association of Muslims which is affiliated with the Islamic Society of North America (ISNA), stated in a press release.
  Muslims in Philippines will celebrate Eid on Tuesday as the official date of the end of Ramadan has been set as 29 July. The Philippine Government in their proclamation had declared 29 July as holiday throughout the country in observance of Eid al-Fitr.

So the question is , is it really possible for people living in different part of the world to see or not see the new moon (0.8% waxing crescent) to mark their festive seasons at different dates?

In other words do Automated calculations \ Lunar calendars give an exact picture of the moon sighting as viewed by a person on earth.

Note : These cultures put personal observation of the new moon a pre requisite to mark the months hence the motivation of this question.


texts: Can moons exist inside a planet's roche limit?

texts: Saturn's rings are inside its own Roche Limit - the limit beyond which bodies start disintegrating due to the tidal forces of the parent body. But as every rock in the ring can be regarded as a satellite of Saturn, why are they not disintegrated to smaller constituents? Also, is it possible for a body to hold itself together even within the Roche Limit (maybe due to some cohesive forces holding it together)? I thought it may be the reason for the rocks in Saturn's rings holding themselves together- but then again, I have no reason to believe it may be the case any way. Can someone provide an estimate for what the cohesive forces may be for a metallic rock as a fraction of the internal gravitational forces in it?


texts: The majority of hot stars originate as binaries or multiple systems. How is it with the cooler spectral types? Are they usually born as single stars?


texts: Is there any significant time dilation on other planets orbiting the sun?

texts: Is there significant time dilation on the other planets orbiting the sun?  Would an 'hour' experienced on earth actually be 59 or 61 minutes on other planets, depending on their distance to the sun?  What about the moons orbiting Jupiter?


texts: Does a black hole become a normal star again?

texts:
Stars which exceed the Tolman-Oppenheimer-Volkoff limit can become a black hole.

What happens to star after it becomes a black hole?
Does it regain its status of star?


texts:
I guess this is more a question about stellar models than anything else. I was wondering what is predicted to be the hottest possible stars that would still be hydrogen-burning.

What complicates this more is that the most massive stars will probably only sit close to the main sequence (as very early O-type) for several thousand years before gaining a WNh spectrum despite still being relatively early in the lifetime. So I'll be somewhat more precise and ask what is the hottest possible star predicted at ZAMS that won't just blow itself apart by radiation pressure.

Also tangential to the topic but have there been any stars found with an O1 spectrum, and is this even a spectral type that has models made for it?


texts: In which direction does the Milky Way rotate?

texts:
We don't have a photo of our Milky Way the whole, all the pictures are artists' interpretations showing a bulge, a central bar, and several spiral arms. The milky way is spinning. I would like to know:

a) Does it spin with the arms trailing or leading?

b) I read if the direction of spin clockwise or counterclockwise depends on whether the Milky Way is observed from above or below. I don't understand how the direction of spin (clockwise & counterclockwise) depends on the point of view of the observer.


texts: How is distance in light-years converted to years back in time?

texts:
When I look at the Alnitak,the left most star of Orion's belt, it is 736 light years away. How could I convert this distance to an estimate of how long ago what I am seeing happened.

Would it be simply be 736 years ago?

Are there instances of when this isn't as straight forward?


texts: Percent-illumination of crescent moon and its naked-eye visibility?

texts:
What level of percent-illumination of moon (waxing crescent), given by Stellarium, is enough to make it visible with naked eye, in clear sky?

thanks


texts:
I have read in a magazine that a star can actually form back to a planet... is it true?!
Does it mean all the planets in our galaxy can be revived back to what they were before?


texts: If there are neutron stars, would most stars be considered "proton stars"?

texts:
For example, the Sun is a giant sphere of positively charged plasma. About 72% of the elements in it are protium. This means that these protium atoms would have had to lose their electrons, right? If so, the majority of the Sun would be protons. So just as there are neutron stars, would stars like our Sun be considered "proton stars"?

This may be a stupid question, but what I'm really getting at is: are stars mostly protons? Is what I described how it all works?


texts: What is the physical geometry of this apparent "eclipse" of a tiny moon of Asteroid Florence?

texts:
Below is a small GIF made from a small subset of images contained in the original 36MB GIF found at https://cneos.jpl.nasa.gov/images/news/florence.p5us.1Hz.s382.sep01.gif as I just found in the Sky and Telescope article Asteroid Florence Has Two Moons.

Although it's tempting to interpret the image as an optical image, I belive this is pulsed-doppler data from the Goldstone Deep Space Network center. I am guessing that one axis is range (delay) and the other is doppler shift.

Still I can't figure out the geometry that would produce an "eclipse" (in this case the moon passing behind the larger asteroid) with it disappearing so "far" from the asteroid.

Could someone help me out here? Is one axis delay (time) and the other doppler shift? One can start with this description but there is more to it than is discussed there.

below: "A radar image shows asteroid 3122 Florence and tiny echoes from its two moons. Here is an animation that shows them more clearly. The direction of the radar illumination (and thus the direction toward Earth) is at the top." From here. NASA / Jet Propulsion Laboratory. This is a small subset of the frames contained in the original 36 MB GIF, and the size has been decreased by a factor of 2 in order to fit in SE's 2 MB limit.


texts: Are there equal number of planets, stars, galaxies etc in observable universe spinning in both directions?

texts: Just because we observed that our milky way galaxy is spinning in a certain direction therefore we assume it is applicable to all other galaxies, I am curious to find out if hypothetically most of the celestial objects such as natural satellites, planets, stars even galaxies within our observable universe are spinning/rotating in the same direction as the milky way what kind of implications can we say about the condition in the early universe? or is it just an coincident?


texts: What would the view be list from TRAPPIST-1g, looking back towards TRAPPIST-1?

texts:
There's a lot of interest with the recent discovery of seven earth sized planets around TRAPPIST-1. I saw this poster, and the NASA video says that in the system you could see a lot of other planets whipping around in their orbits.

It got me wondering:

Obviously that poster is exaggerated, but how exaggerated?
What would you actually see with the naked eye, standing on TRAPPIST-1g, and looking back toward the other planets?
How big would they appear?
What might TRAPPIST-1 look like?


texts: Why isn't our local interstellar space colorised?

texts:
Looking at answers to this question, people seem pretty convinced that human naked eye should be able to see the colour of ionised gas/dust cloud when they are inside an emission nebula.

And we know Solar system is surrounded by Interplanetary dust cloud, and possibly inside an Interstellar cloud. Why don't we see a colorised space backdrop?

Does it have to do with density of gas cloud? or how ionised they are? Does camera with long exposure see some background colour our naked eye can't?

(Excuse me for any wrong terminology.)


texts: How to convert factors of time dilation into something relatable?

texts:
On this post,

Time according to the gravity of Sagittarius A?

They found the factor of time on the varying distances from the SMBH, I am curious on how to turn those factors into relatable terms such as:
At 1 km from the event horizon ____ time passes on earth in an hour.

I'm just not sure how to figure this out.


texts:
Planet A and Planet B orbit a sun-like star.  Planet A has a semi-major axis of 1 AU from the star.  Planet B has an albedo of .8 and has the same radius as Jupiter.  When Planet B is observed from Planet A when the planets are at opposition (Planet B is directly opposite from the star from the perspective of Planet A), Planet B has an apparent magnitude of 4

How far is Planet A from Planet B?  (alternatively, what is the semi major axis of Planet B?)

Assume negligible eccentricity in the orbits.  Assume co-planar orbits.


texts: What's to be gained from the New Horizons mission once it's beyond the Kuiper Belt?

texts: Now that we have seen what Pluto has to offer and New Horizons is headed to the Kuiper Belt, is there anything we can gain from the mission in interstellar space after it travels beyond the Kuiper Belt?


texts:
What is meant by the "mini disk" of a blackhole? Is it the same as accretion disk? If not, whats the difference?

Eg: In the abstract of this paper https://arxiv.org/abs/1806.05697 it is mentioned "When the accretion rate is relatively high, the circumbinary disk, accretion streams, and mini-disks combine to emit light in the UV/EUV bands"


texts: Eclipse Visible Light Not Dark as Expected

texts: I live in a place where we weren't on the path of totality but were in the 90% range. I was expecting it to be a lot darker than it ended up being. What does it mean to be in the 90% range on this map? I was expecting it to block out 90% of the visible light, but while it was noticeably dimmer it wasn't close to what I thought 10% of light would look like.


texts: Is nuclear pasta or neutron star crust iron stable outside of neutron stars?

texts: When neutron stars collide, they crash into and kill each other in a kilonova explosion, which blasts a lot of their material into space. A huge amount of neutronium, neutron star stuff, is suddenly no longer in the high pressure of the star, and instantly expands explosively into normal matter. In other words, thou shalt not have isolated teaspoons of neutronium. But is the same true for the crust, made of a form of highly compressed iron called nuclear pasta, 10 billion times stronger than steel? Is the crust material of neutron stars stable outside of neutron stars?


texts: Are any other planetary bodies warming up as well in the Solar System?

texts: Do we have a few decades worth of surface temperature data to compare?


texts: VSOP87D: What are the purpose of the initial columns in the VSOP87D data?

texts:
I am trying to write an app to determine planetary positions, using Jean Meeus' Astronomical Algorithms as a reference. His guidance on using the VSOP87D data is straightforward, as are many other sources that I googled. But all of these talk only about the last three columns of that data. What is the purpose of the preceding columns? Some are self explanatory (e.g., the simple numbering of each row), but others seem to have no explanation either in the file itself or the 'read me' documents that accompany it on the FTP site. I want to ensure I fully understand the data.

Here is an example of the third row of VSOP87D for the planet Jupiter:

4510, 3, 0, 0, 0, 0, 2, -5, 0, 0, 0, 0, 0, 0, -0.00566632795, -0.00089195704, 0.00573610145, 1.44406205976, 7.11354700080

where I have replaced the various spaces with commas to save space.

I will note that the term .00573610145, for example, differs by by several orders of magnitude from that listed in Meeus' table, as do some other terms. But this does not seem to correspond to any of the numbers in the other columns, unless I'm missing the obvious.

The data is taken from the FTP website: ftp://cdsarc.u-strasbg.fr/pub/cats/VI%2F81/VSOP87D.jup

Thanks!


texts:
In a textbook, we have an example:

The density of matter in the interstellar medium is of order one
proton per ${\rm cm^3}$, then the total mass of the interstellar
medium is of order (The $10^6$ term accounts for the number cubic
centimetres within one meter cubed). \begin{equation} m=1\times
V_\text{galaxy}\times m_\text{P}\times
10^6=3.3\times10^{40}{\rm kg}\approx 17 \cdot 10^9 M_{\odot}
> \end{equation}

So I was wondering, should the unit of the equation be:
$\frac{{1}}{{\rm cm^3}}\times{\rm m^3}\times{\rm kg}$?
And what exactly should be the unit of proton in the formula? Should it be unitless? Or ${\rm kg}$? Thank you.
Source: Beech, M. (2019). Introducing the stars. Cham: Springer Nature Switzerland AG.


texts: Not able to get Perfect Focus with DSLR and Newtonian

texts:
When using DSLR with Newtonian (130mm/1000mm), I am not able to get perfect focus.
However, when I use an eyepiece, I am able to get crystal clear views. So, I think collimation is okay.
The focusing tube is not short. I am able to focus upto a certain point using the DSLR. But the best focus that I am able to get is not crystal clear.
Any suggestions?
Thanks!


texts: Earth orbit around the Sun and its position in the Galaxy

texts: Given the orbit of the Earth around the Sun and the position of the Sun in the Galaxy, in which season are we (the Earth) closer to the galactic center?


texts: How do or could radio telescopes contribute to exoplanet studies?

texts: Current and upcoming telescopes which find exoplanets and take spectra of their atmospheres seem to be optical or infrared. What about radio telescopes applied to exoplanets? They are larger and more easy to use with interferometry. Why aren't radio frequencies as useful as optical/IR for exoplanet studies?


texts: Do the number of moons a planet has affect the speed of the planet's rotation?

texts: Would the tidal forces of multiple moons interacting upon a planet speed up or slow down the day length of the planet? I was thinking that maybe the planet's day length would be slowed down due to all of the gravitational tugging, but on the other hand I was thinking that maybe all of those tidal forces could perhaps slingshot the planet ahead and make it spin at a faster rate. Would the day length even change at all? If the answer is yes, could all of those moons even affect the planet's precession?


texts: Capability of observing transits with terrestrial telescopes of various sizes?

texts:
I have access to my university's telescope, Dearborn Observatory, an 18.5 inch refractor on the shore of Lake Michigan, just north of Chicago (yes, it's an atrocious location, but the telescope still works fantastically given this), and I was wondering if it would be possible to detect exoplanet transits.  I have access to a CCD.  Obviously, normally this would take quite a while, but I was looking at Wikipedia's list of transiting exoplanets and several of them have periods of less than 10 hours or so.

Are there any good resources about the math for this?  Or is the approximation that size of the change in light observed by the transit is just using the ratio of the area that the planet occludes to the area of the host star a reasonably good approximation?

Or is observing the transits of any known exoplanets completely unfeasible with this size of telescope?  From previous nights of photographing the sky, it seems like the telescope's limit is roughly magnitude 13-15, beyond which the signal-to-noise ratio is just too low to get meaningful data.


texts: Does the earth's atmosphere act as a spherical lens and refract light from space?

texts:
If so by how much does it "spoil" the view of stars and galaxies etc.

Is this error noticable, when compared to pictures taken from outer space.


texts:
I did read several of the Oort Cloud questions/answers which I found very helpful and instructive, but this question still persists for me:

Is the Oort Cloud actually opaque, or is the "cloud" used euphemistically because minor planets inside of it are too dim to be seen?


texts: Is it possible that the Universe is expanding due to additional Big Bang events?

texts:
Is it theoretically possible that the Universe is expanding due to additional Big Bang events that have occurred at the same location that the original Big Bang occurred at?

Perhaps there has been an ongoing series of smaller Big Bang events over the past 13.7 billion years, which although were not as massive in scale as the original Big Bang, have created a large amount of new space-time and new matter that has resulted in the Universe expanding.


texts: How to send information from the far side of the Moon to the Earth?

texts: Chang-E has just sent a shot after landing on the far side of the moon. It looks tricky, how  can a device send information from a place that is oriented opposed to Earth?


texts: Can Drizzle Integration increase resolution beyond theoretical resolution of telescope?

texts:
So I was wondering, if drizzle integration actually increases details in your image if the drizzled image results in higher resolution in terms of arcseconds / pixel than the telescope would allow (due to the uncertainty principle the telescope's resolving capability is dependent on its diameter, more commonly referred to as the diffraction limit 1, 2 )

In my case I have around 0.52" per px on my main camera and my GSO RC8" allows for around 0.5" resolution max due to the uncertainty principle. Drizzling an image would then give me 0.26" per px on the drizzled image when increasing width and height of the image by factor 2, which is higher resolving power than what the telescope would actually be able to do.

Apart from sharper and more defined stars when drizzle integrating, will drizzle integration actually increase my resolving capability?


texts: What is the danger for Ceres of collision with other asteroids?

texts: In the context of possible colonization of Ceres, would not such colony be totally impossible because of high probability of collision of Ceres with other asteroids in the Asteroid Belt?


texts:
I'm working with flickering measures from some stars. So, I take differential magnitudes, make a histogram and fit their standard deviation. My measure of flickering is the FWHM (full width at half maximum).
But I don't know how to analyze the noise. A full goal would be to measure the standard deviation of noise and discount this to FWHM. An acceptable goal would be to show that  FWHM is due mainly to signal and not to noise.
I'm following A comparative study of the strength of flickering in cataclysmic variables by Albert Bruch, but I'm not studying CVs.


texts: Enhanced Star-Gazing with Special Glasses

texts:
I watched a video yesterday on how telescopes not only magnify images but also increase the amount of light entering into your eye, allowing you to see things not normally visible with naked eye. Would it be possible to create a "telescope" with no magnification, a wide field of view... say ~190 degrees left/right, ~120 degrees up/down (the average human field of view), and small enough to wear? Essentially creating glasses that allow for better star gazing?

A side question is do night vision goggles let you see more stars? or does the increase in ambient light from earthly objects negate any increase.


texts: What is behind the Great Red Spot's longevity?

texts: On Earth, storms can last a few days. The Great Red Spot on Jupiter is a storm that has been going on for more than 400 years now. What is different on Jupiter that makes it possible for storms to last so long?


texts: I assume that the A ring is the densest, but I might be wrong. Nevertheless, I failed to find any explicit information over the net about the minimum and maximum of densities for the different rings. As a less practical question: what would one see upon entering one of the denser rings? Would it be obvious that it is a dense but thin (few metres - 1 km) cloud of particles, continuously bombarding the spacecraft irregardless whether it orbits along within the ring, or one would not see more than just a distant haze (if lit by the Sun) that spans over the horizon?


texts: How to interpret extreme ultraviolet/ x-ray data in the literature?

texts: I am interested in a sun-like star 138 light years away that is in the EUVE catalog. A table shows that a photon count of 2.6+/-0.5 photons per kilosecond at 100 angstroms has been detected for this star. I can not determine if this is high or not. I am even having a hard time finding what solar emission is at this wavelength so i can attempt the math to compare with the sun. Can somebody help me here?


texts: Does time also pass more slowly for a galaxy that is traveling at relativistic speeds, where the speed difference is due to Hubble expansion?

texts: If time passes more slowly, relative to Earth, for a traveler at relativistic speeds, say at .8c, traveling between stars inside this galaxy, does time also pass more slowly for a distant galaxy that is moving away at relativistic speeds, where the speed difference is due to the Hubble expansion of space?


texts:
what is our Solar System called rather than "the Solar System"?

I've found "Sol System" and "Monmatia", too, but is there more to it?


texts:
I am wondering about what is the estimated size of astrophysical jet that shoots out from a black hole, I don’t know if it is determined by the size of a black hole.

What would classify a black hole that is able to have at least 10 planets orbit it? Is it considered stellar?

If so, what would the estimated astrophysical jet or quasar be?


texts:
The Z/A term for calculations of degeneracy pressure for white dwarfs is given as 0.5. But I can't find an explanation as to why. For my assignment, I am trying to find the degeneracy pressure for the core of the sun. I am given R = 0.1Rsun and M = 0.1Msun. I am also told that the core contains 50% hydrogen and 50% helium.

I need to find Z/A for this scenario in order to find the degeneracy pressure, but I don't know how to approach it.


texts:
If my understanding is correct, Chury, the best explored comet so far is rather on the smallish side as comets go. Most comets observable with naked eye were so because they flew close to Earth, not because they were so big. I wonder, though, how big are the biggest ones.

Let's get it in two variants:

How big is the biggest known comet? (mass, diameter)
Is there an estimate, or a theoretical limit on how big a comet can be? (for whatever reason, e.g. becoming a planet, breaking up due to tidal forces or whatever)


texts: Can you tell me about Flamsteed numbers? I just know that it is a specific number used for identification of stars. But what is the theory behind it? In what way is the number given to stars?


texts: The CNO cycle in first generation of stars

texts:
I'm an undergrad interested in astophysics and this question struck my mind:

As the CNO cycle requires carbon to start, and carbon is produced by thermonuclear fusion in stars, is it fair to think that the hotter stars in the first generation didn't have a CNO cycle?
Or should I instead think that the first generation of stars had an initial metalicity and therefore the CNO cycle was possible?


texts:
Why doesn't the earth have a ring?

If solid material such as dust and moonlets, and common components of satellite systems are brought nearer to the Earth, then what will happen? Will it take the form of a ring or fall down on the Earth?


texts: Why haven't detected life in the universe?

texts: It would seem that if life were relatively common in the universe that there would be a cacophony of noise somewhere in the electromagnetic spectrum. Is life so rare and distant that the waves haven't reached us yet, or have they attenuate out, or are they unintelligible, or are we the first, or are we alone?


texts: What is the difference between $E_\gamma$ and $E_{\gamma,iso}$ in gamma ray bursts?

texts:
In the literature on gamma ray bursts I see several references to $E_\gamma$ and $E_{\gamma,iso}$ for example as in Piran (2005)

$E_{k,iso,52}$ is “isotropic equivalent” kinetic energy,
discussed below, in units of 1052 ergs, while $E_{k,θ,52}$ is the real kinetic energy in the jet i.e:
$E_{k,θ,52} = (θ^2/2)$$E_{k,iso,52}$. One has to be careful which of the two energies one discusses. In
the following I will usually consider, unless specifically mentioned differently, $E_{k,iso,52}$, which
is also related to the energy per unit solid angle as: $E_{k,iso,52}/4π$

My interpretation is that when an observation of a GRB is made, an energy $E$ is recorded. $E_{\gamma,iso}$ is the total energy that would have been emitted by the explosion if the energy was released equally in all directions and by considering our distance away from it. However, because we know that GRBs are tightly beamed, $E_\gamma$ is the corrected energy by taking $E_{\gamma,iso}$ and considering only a small fraction of it in a tight beam. However, this all seems a tad confusing and I can't see the point in talking about $E_{\gamma,iso}$ when we think they are very tightly beamed.
I would appreciate some clarification on what exactly $E_\gamma$ and $E_{\gamma, iso}$ are and where they come from.
Thanks


texts: From original burst, fraction of stellar mass still surviving on Main sequence

texts:
Suppose that all stars in this galaxy were born in a single major-merger burst event about 10
Gyr ago. From this original burst, I want to compute the fraction of stellar mass still surviving as stars in the
main sequence ? For this, I have got to use a Salpeter IMF, and a star formation range between 0.1 and 120 solar
masses.

What I have done is starting from Salpeter IMF : $$\Phi(m)\text{d}m=\Phi_{0}\,m^{-2.35}$$

with $$\Phi_{0}$$ a constant normalization.

From this, I integrate from $$m_{1}=0.1\,\text{M}_{\odot}$$ to $$m_{2}=120\,\text{M}_{\odot}$$

$$N(0.1<m<120) = \int_{0.1}^{120}\,\Phi(m)\,\text{d}m = \Phi_{0}\,\bigg[\dfrac{0.1^{-1.35}-120^{-1.35}}{1.35}\bigg]$$

This result depends on the valeur of $$\Phi_{0}$$ and I don't know how to deal with it in order to get $$N(0.1<m<120)$$ ?

Moreover, it seems that I have to take into account of the age of the major-merger burst event (10 Gyr).

From these 2 principles, how could I calculate the fraction of stars surviving in the main sequence ?

Any help is wlecome, Regards